U.S. patent number 8,333,239 [Application Number 12/687,711] was granted by the patent office on 2012-12-18 for apparatus and method for downhole steam generation and enhanced oil recovery.
This patent grant is currently assigned to Resource Innovations Inc.. Invention is credited to Fred Schneider, Lynn P. Tessier.
United States Patent |
8,333,239 |
Schneider , et al. |
December 18, 2012 |
Apparatus and method for downhole steam generation and enhanced oil
recovery
Abstract
A burner with a casing seal is used to create a combustion
cavity at a temperature sufficient to reservoir sand. The burner
creates and sustains hot combustion gases at a steady state for
flowing into and permeating through a target zone. The casing seal
isolates the combustion cavity from the cased wellbore and forms a
sealed casing annulus between the cased wellbore and the burner.
Water is injected into the target zone, above the combustion
cavity, through the sealed casing annulus. The injected water
permeates laterally and cools the reservoir adjacent the wellbore,
and the wellbore from the heat of the hot combustion gases. The hot
combustion gases and the water in the reservoir interact to form a
drive front in a hydrocarbon reservoir.
Inventors: |
Schneider; Fred (Calgary,
CA), Tessier; Lynn P. (Eckville, CA) |
Assignee: |
Resource Innovations Inc.
(Calgary, CA)
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Family
ID: |
42336027 |
Appl.
No.: |
12/687,711 |
Filed: |
January 14, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100181069 A1 |
Jul 22, 2010 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61145501 |
Jan 16, 2009 |
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Current U.S.
Class: |
166/261; 277/355;
166/305.1; 166/302 |
Current CPC
Class: |
E21B
43/20 (20130101); E21B 43/243 (20130101); E21B
36/02 (20130101) |
Current International
Class: |
E21B
43/24 (20060101); E21B 36/00 (20060101) |
Field of
Search: |
;166/256,261,302,305.1
;277/355 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Latii, M.J., and Le Thiez, P.A., Numerical Evaluation of CO2
Effects in Thermal Oil Recovery Processes, Society of Petroleum
Engineers/US Department of Energy Document #24170, 1992. cited by
other .
Precision Combustion, Inc., News webpage, PCI Developing Downhole
Catalytic Combustor Steam Generator for Heavy Oil Production, May
2, 2006. cited by other .
Garfield, Garry, and Mackenzie, Gordon, Recent Metal-to-Metal
Sealing Technology for Zonal Isolation Applications Demonstrates
Potential for Use in Hostile HP/HT Environments, 2007. cited by
other.
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Primary Examiner: Gay; Jennifer H
Assistant Examiner: Loikith; Catherine
Attorney, Agent or Firm: Goodwin; Sean W.
Claims
The embodiments of the invention for which an exclusive property or
privilege is claimed are defined as follows:
1. A process for creating a drive front in a hydrocarbon reservoir
for enhanced oil recovery comprising the steps of: positioning a
burner assembly within a target zone in the hydrocarbon reservoir;
creating a combustion cavity in the target zone with the burner
assembly downhole of the burner assembly; creating and sustaining
hot combustion gases with the burner assembly for entering into and
permeating through the target zone from the combustion cavity; and
injecting water into the target zone uphole of the burner assembly,
for permeating through the target zone and interacting with the hot
combustion gases therein for creating steam and a steam drive front
in the formation.
2. The process of claim 1, wherein the creating and sustaining of
the hot combustion gases further comprises combusting at
sub-stoichiometric conditions.
3. The process of claim 1, wherein the hydrocarbon reservoir is
accessed with a cased wellbore, further comprising forming a casing
annulus between the burner assembly and the cased wellbore, and
sealing the casing annulus uphole of the combustion cavity.
4. The process of claim 3, wherein injecting the water into the
target zone further comprises injecting water through the casing
annulus.
5. The process of claim 1, wherein injecting the water into the
target zone further comprises cooling an upper portion of the
hydrocarbon reservoir adjacent a cased wellbore.
6. The process of claim 1, wherein injecting the water into the
target zone further comprises cooling a cased wellbore.
7. The process of claim 1, wherein injecting the water into the
target zone further comprises injecting water from the burner
assembly.
8. The process of claim 1, wherein creating a combustion cavity
further comprises creating a combustion cavity having a
substantially impermeable base and permeable lateral walls.
9. The process of claim 1, wherein the hydrocarbon reservoir is
accessed with a cased wellbore and wherein positioning the burner
assembly within a target zone further comprises: running a main
tubing string, a torque anchor and the burner assembly downhole
into the cased wellbore and setting the torque anchor with the
burner assembly within the target zone, a casing annulus being
formed therebetween; and running an intermediate tubing string
downhole within a main bore of the main tubing string and fluidly
connecting the intermediate tubing string to the burner assembly,
the intermediate tubing string having an intermediate bore and
forming an intermediate annulus between the main tubing string and
the intermediate tubing string, wherein discrete passageways are
provided for supplying water, fuel and oxygen to the burner
assembly.
10. The process of claim 9 further comprising releaseably
connecting the intermediate tubing string to the main tubing
string.
11. The process of claim 9 further comprising: running an inner
tubing string downhole within the intermediate bore of the
intermediate tubing string and fluidly connecting the inner tubing
string to the burner assembly, the inner tubing string having an
inner bore and forming an inner annulus between the intermediate
tubing string and the inner tubing string, wherein discrete
passageways are provided for supplying at least water, fuel and
oxygen to the burner assembly.
12. The process of claim 11 further comprising releaseably
connecting the inner tubing string to the intermediate tubing
string.
13. The process of claim 11 further comprising: releaseably
connecting the inner tubing string to the intermediate tubing
string; stretching the inner tubing string; hanging the inner
tubing string; and cutting the inner tubing string to an
appropriate length.
14. The process of claim 9 further comprising: releaseably
connecting the intermediate tubing string to the main tubing
string; stretching the intermediate tubing string; hanging the
intermediate tubing string; and cutting the intermediate tubing
string to an appropriate length.
15. The process of claim 1, wherein creating a combustion cavity in
the target zone with the burner assembly further comprises creating
the combustion cavity at a temperature sufficient to melt the
reservoir.
16. A downhole steam generator for enhanced oil recovery from a
hydrocarbon reservoir accessed by a cased and completed wellbore
having a wellhead, comprising: a main tubing string fluidly
connected to the wellhead and supported in the cased wellbore; at
least an intermediate tubing string having an intermediate bore and
disposed within a main bore of the main tubing string for forming
an intermediate annulus therebetween, the main bore and the
intermediate annulus forming at least two fluid passageways; a
burner assembly within the cased wellbore positioned at the
hydrocarbon reservoir, the burner assembly having a downhole burner
and a burner interface assembly for fluidly connecting the downhole
burner to at least the main tubing string and the intermediate
tubing string for fluidly connecting the burner assembly to the
wellhead the burner interface assembly further comprising an outer
housing fluidly connected at an uphole end with the main tubing
string and fluidly connected by the intermediate annulus at a
downhole end with the downhole burner, an intermediate mandrel
connected at an uphole end with the intermediate tubing string and
fluidly connecting the intermediate bore at a downhole end with the
downhole burner, the intermediate mandrel fir within the outer
housing, and an intermediate latch assembly between the outer
housing and the intermediate mandrel for releasably connecting
therebetween; a high temperature casing seal adapted for sealing a
casing annulus between the downhole burner and the cased wellbore;
and means for injection of water to the hydrocarbon reservoir above
the casing seal.
17. The generator of claim 16 wherein the casing seal is a brush
seal.
18. The generator of claim 17, wherein the brush seal further
comprises a stack of a plurality of flexible brush rings.
19. The generator of claim 18, wherein each of the plurality of
flexible brush rings comprises an annular ring having a
multiplicity of circumferentially spaced, radially inwardly
extending slits forming flexible fingers.
20. The generator of claim 19, wherein each of the flexible brush
rings are rotationally indexed from one another to misalign slits
of the adjacent brush rings.
21. The generator of claim 16 wherein at least a third passageway
is connected to the downhole burner, further comprising: an inner
tubing string disposed within the intermediate bore of the
intermediate tubing string for forming an inner annulus
therebetween, the inner tubing string having an inner bore, the
intermediate tubing string and inner tubing string fluidly
connecting the burner assembly to the wellhead; and wherein the
burner interface assembly further comprises: an inner mandrel
connected an uphole end to the inner tubing string and fluidly
connecting the inner bore at a downhole end with the downhole
burner, the inner mandrel fit within the intermediate mandrel; and
an inner latch assembly between the intermediate mandrel and the
inner mandrel for releaseably connecting therebetween.
22. The generator of claim 21 wherein the intermediate tubing
string is an intermediate coil tubing string and the inner tubing
string is an inner coil tubing string.
23. The generator of claim 21, wherein the inner annulus is sealed
at the burner interface assembly for the detection leaks from the
intermediate annulus, the inner bore, or a combination thereof.
24. The generator of claim 21, wherein the burner interface
assembly further comprises a backpressure valve assembly for at
least one of, or both of, the at least two passageways for fuel and
oxygen.
25. The generator of claim 24, wherein the backpressure valve
assembly further comprises a first bypass passageway having a first
backpressure valve for fuel and a second bypass passageway having a
second backpressure valve for oxygen.
26. The generator of claim 21, wherein the intermediate annulus
fluidly communicates fuel to the downhole burner and wherein the
inner bore fluidly communicates oxygen to the downhole burner.
27. A process for creating a drive front in a hydrocarbon reservoir
accessed with a cased wellbore for enhanced oil recovery comprising
the steps of: positioning a burner assembly within a target zone in
the hydrocarbon reservoir, wherein running a main tubing string, a
torque anchor and the burner assembly downhole into the cased
wellbore and setting the torque anchor with the burner assembly
within the target zone, a casing annulus being formed therebetween;
and running an intermediate tubing string downhole within a main
bore of the main tubing string and fluidly connecting the
intermediate tubing string to the burner assembly, the intermediate
tubing string having an intermediate bore and forming an
intermediate annulus between the main tubing string and the
intermediate tubing string, creating a combustion cavity in the
target zone downhole of the burner assembly; creating and
sustaining hot combustion gases with the burner assembly for
flowing from the combustion cavity and into the target zone; and
injecting water into the target zone, for interacting with the hot
combustion gases and conversion into steam for creating the drive
front.
28. The process of claim 27 further comprising: running an inner
tubing string downhole within the intermediate bore of the
intermediate tubing string and fluidly connecting the inner tubing
string to the burner assembly, the inner tubing string having an
inner bore and forming an inner annulus between the intermediate
tubing string and the inner tubing string, wherein discrete
passageways are provided for supplying at least water, fuel and
oxygen to the burner assembly.
29. The process of claim 27 further comprising: releaseably
connecting the intermediate tubing string to the main tubing
string; stretching the intermediate tubing string; hanging the
intermediate tubing string; and cutting the intermediate tubing
string to an appropriate length.
30. A downhole steam generator for enhanced oil recovery from a
hydrocarbon reservoir accessed by a cased and completed wellbore
comprising: a burner assembly within the cased wellbore positioned
at the hydrocarbon reservoir, the burner assembly having a downhole
burner; a high temperature brush seal having a stack of a plurality
of flexible brush rings, the brush seal being adapted for sealing a
casing annulus between the downhole burner and the cased wellbore,
each flexible brush ring comprising an annular ring having a
multiplicity of circumferentially space, radially inwardly
extending slits which are rotationally indexed from one another to
misalign slits of the adjacent annular ring; and means for
injection of water into the hydrocarbon reservoir above the brush
seal.
31. The generator of claim 30, wherein the radially inwardly
extending slits are clockwise oriented spiral slits.
32. The generator of claim 30, further comprising spacer rings
between each of the brush rings.
Description
FIELD OF THE INVENTION
The present invention relates to an apparatus and a method for
creating a drive front for enhanced oil recovery. More
specifically, a downhole burner first forms a combustion cavity in
a hydrocarbon formation and then a combination of steady state
combustion and water injection above the cavity creates a steam and
gas drive front in the hydrocarbon formation.
BACKGROUND OF THE INVENTION
It is known to conduct enhanced oil recovery (EOR) of hydrocarbons
from subterranean hydrocarbon formations after primary recovery
processes are no longer feasible. EOR include thermal methods such
as in-situ combustion, steam flood, and miscible flooding which use
various arrangements of stimulation or injection wells and
production wells. In some techniques the stimulation and production
wells may serve both duties. Other techniques include steam
flooding, cyclic steam stimulation (CSS), in-situ combustion and
steam assisted gravity drainage (SAGD). SAGD uses closely coupled,
a horizontally-extending steam injection well forming a steam
chamber for mobilizing heavy oil for recovery at a substantially
parallel and horizontally-extending production well.
Thermal methods of EOR can only be implemented in wells that have
been completed for thermal completions. Due to the high
temperatures used in thermal completions, wells employing such EOR
techniques must be completed using materials, such as steel and
cement, that can withstand high temperatures. Wells that were not
completed with such high temperature resistant materials cannot
implement thermal completions for EOR. Accordingly, well operators
must decide on whether or not to implement of thermal EOR and based
on this decision complete a well using (or not) high temperature
resistant materials.
U.S. Pat. No. 3,196,945 to Forrest et al (assigned to Pan American
Petroleum Company) discloses a downhole process comprising a first
igniting a reservoir and then injecting air or an equivalent oxygen
containing gas in an amount sufficient to create a definite
combustion zone or front, the front being at high temperature,
typically 800-2400.degree. F. Called forward combustion, Forrest
contemplates an oxygen rich front for continued combustion. Demands
for large air flow is reduced by co-injection of water or other
suitable condensable fluid into the heated formation to create
steam front that urges the movement of hydrocarbons or oil. Forrest
can co-discharge water and air to the heated formation for creating
high temperature steam.
U.S. Pat. No. 4,442,898 to Wyatt (assigned to Trans-Texas Energy
Inc.) discloses a downhole vapor generator or burner. High pressure
water in an annular sleeve around the burner combustion chamber
within which an oxidant and fuel are combusted. The energy from the
combustion vaporizes the water surrounding the combustion chamber,
cooling the burner and also creating high temperature steam for
injection into the formation.
U.S. Pat. No. 4,377,205 to Retallick discloses a catalytic low
pressure combustor for generating steam downhole. The steam
produced from the metal catalytic supports is conducted to steam
generating tubes, and the steam is injected into the formation. Any
combustion gases produced are vented to the surface.
U.S. Pat. No. 4,336,839 to Wagner et al (assigned to Rockwell
International corp.) discloses a direct firing downhole steam
generator comprising an injector assembly axially connected with a
combustion chamber. The combustion products, including CO.sub.2,
are passed through a heat exchanger where they mix with pre-heated
water and are ejected out of the generator into the formation
through a nozzle.
U.S. Pat. No. 4,648,835 to Eisenhawer et al. (assigned to Enhanced
Energy Systems) discloses a direct fire steam generator comprising
a downhole burner employing a unique ignition technique using the
gaseous injection of a pyrophoric compound such as triethylborane.
Natural gas is burned and water is introduced to control
combustion. The combustion products, like in Wagner are mixed with
water and the resulting steam and other remaining combustion
products are injected into the formation.
US Patent Application Publication 2007/0193748 to Ware et al
(assigned to World Energy Systems, Inc.) discloses a downhole
burner for producing hydrocarbons from a heavy-oil formation.
Hydrogen, oxygen and steam are pumped by separate conduits to the
burner. A portion of the hydrogen is combusted and the burner
forces the combustion products out into the formation. Incomplete
combustion is useful in suppressing the formation of coke. The
injected steam cools the burner, thereby creating a super heated
steam which is also injected into the formation along with the
combustion products. CO.sub.2 from the surface is also pumped
downhole for heating and injection into the formation to solubilise
in oil for reducing its viscosity.
In-situ processes to date have not successfully provided economic
solutions and have not resolved issues of temperature management,
corrosion, coking and overhead associated with existing surface
equipment.
SUMMARY OF THE INVENTION
The present invention is an apparatus and method of creating a
drive front in a hydrocarbon reservoir. The apparatus is positioned
in a cased wellbore within a target zone in the hydrocarbon
reservoir. The apparatus comprises a downhole burner fluidly
connected to a tubing string extending downhole. The tubing string
comprises a plurality of passages for at least fuel, and oxidant
and water. The downhole burner creates a combustion cavity within
the target reservoir zone by combusting the fuel and the oxidant,
such as oxygen, at a temperature sufficient to melt the reservoir
at the target zone or otherwise form a cavity below the downhole
burner. Once the combustion cavity is created, the downhole burner
operates at steady state for creating and sustaining hot combustion
gases in the combustion cavity, which flow or permeate into the
hydrocarbon reservoir. The hot combustion gases permeate away from
the combustion cavity forming a gaseous drive front, transferring
some of its heat to the rest of the reservoir.
Water is also injected into the target zone above the combustion
cavity, which flow or permeate laterally into the reservoir
adjacent the wellbore. In the reservoir, the water acts to cool the
reservoir adjacent the wellbore, decreasing the amount of heat lost
to the overburden. At an interface, the water and hot combustion
gases combine to create a steam and gaseous drive front.
Further, the injection of water adjacent the wellbore also cools
the cased wellbore, protecting the casing against the heat from the
steam and hot combustion gases. Accordingly, the present invention
is not limited to use only in thermally completed wells and can be
implemented at any cased wellbore, whether or not the wellbore was
completed for thermal EOR.
In a broad aspect of the invention, a process for creating a steam
and gas drive front is disclosed. A downhole burner assembly,
fluidly connected to a main tubing string, is positioned within a
target zone in a hydrocarbon reservoir. The burner assembly creates
a combustion cavity by combusting fuel and an oxidant at a
temperature sufficient to melt the reservoir or otherwise create a
cavity. The burner assembly then continues steady state combustion
to create and sustain hot combustion gases for flowing and
permeating into the reservoir for creating a gaseous drive front.
Water is injected into the reservoir, uphole of the combustion
cavity for creating a steam drive front.
In another broad aspect of the invention, a downhole steam
generator for enhanced oil recovery from a hydrocarbon reservoir
accessed by a cased and completed wellbore is disclosed. The
downhole steam generator is a burner assembly positioned within the
cased wellbore at the hydrocarbon reservoir, the burner assembly
having a high temperature casing seal adapted for sealing a casing
annulus between the downhole burner and the cased wellbore, and a
means for injecting water into the hydrocarbon reservoir above the
casing seal. The high temperature casing seal can pass through
casing distortions, and is reusable, not being affected
substantially by thermal cycling.
In another broad aspect of the invention, a system for creating a
drive front in a hydrocarbon reservoir having a cased wellbore is
disclosed. The system has a burner assembly having a downhole
burner and a high temperature casing seal for sealing a casing
annulus between the downhole burner and the casing of the cased
wellbore. The high temperature casing seal can pass through casing
distortions and is reusable, substantially not being affected by
thermal cycling.
In another broad aspect of the invention, a system is provided for
fluidly connecting three concentric passageways in a main tubing
string to a downhole tool. The system has an outer housing, an
intermediate mandrel and an inner mandrel. The outer housing is
releaseably connected to the intermediate mandrel by an
intermediate latch assembly and similarly, the inner mandrel is
releaseably connected to the intermediate mandrel by an inner latch
assembly. The intermediate mandrel is fit within the outer housing,
forming an intermediate annulus therebetween, and is adapted to
fluidly connect to an intermediate tubing string. The inner mandrel
is fit within the intermediate mandrel, forming an inner annulus
therebetween and is adapted to fluidly connect to an inner tubing
string. The inner mandrel further has an inner bore.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a side cross-sectional view of an embodiment of the
present invention, illustrating a combustion cavity in a
hydrocarbon reservoir, the cavity being created by downhole burner
and formed for disseminating hot combustion gases for forming a
gaseous drive front and interacting with water injected uphole of
the cavity for forming an additional steam drive front;
FIG. 2A is a side quarter-sectional view of a wellhead for
supporting three tubing strings extending down a cased wellbore
according to one embodiment of the present invention;
FIG. 2B is a side quarter-sectional elevation of the three tubing
strings of FIG. 2A (casing omitted) and illustrating a main tubing
string supporting the downhole burner at a burner interface
assembly, the main tubing string having an intermediate and an
inner tubing string disposed therein;
FIG. 3 illustrates a quarter-sectional, perspective view across the
casing and three concentric tubing strings;
FIG. 4 is a side quarter-sectional view of an embodiment of a
downhole burner sealed at a downhole end to a casing for fluidly
connecting a casing annulus and the reservoir through
perforations;
FIG. 5 is a side, quarter-sectional view of the burner of FIG. 3
with the casing omitted, and illustrating the fuel passageway, the
oxygen passageway and the nozzle;
FIG. 6 is a side, quarter-sectional view of the burner of FIG. 3
with the casing and oxygen passageway omitted for illustrating the
casing seal and an embodiment of fuel passageway swirl vanes;
FIG. 7A is a partial cross-sectional view of the nozzle and an
embodiment of a brush-type casing seal of FIG. 3 with the casing
omitted;
FIG. 7B illustrates an activated brush seal according to FIG. 7A
and showing the stack of flexible brush rings flexing when
constrained by the casing;
FIG. 8 is a overhead plan view of one concentric brush ring of a
stack of concentric brush rings of a brush seal and an arrangement
of spiral slits and fingers;
FIG. 9 is a perspective view of two brush rings of the stack of
concentric brush rings according to FIG. 8 illustrating a
rotational offsetting of the spiral slits for forming a tortuous,
restrictive fluid path therethrough;
FIG. 10 is a schematic representation a main tubing string, an
intermediate tubing latched within the bore of the main tubing
string, and an inner tubing latched and terminated within the bore
of the intermediate tubing, three fluid passageways created
therein, the inner annulus being terminated at the intermediate
mandrel;
FIG. 11 is a cross-sectional view of the burner interface assembly
illustrating the outer housing, the intermediate and inner
mandrels, the intermediate and inner latch assemblies, and the
backpressure valve assembly;
FIG. 12 is a side quarter-sectional view of an uphole end of the
intermediate mandrel for illustrating termination of the inner and
intermediate tubing and the inner mandrel having an inner tubing
latch;
FIG. 13 is a quarter-sectional and elevation view of a step of the
running in of an embodiment of the apparatus of the invention, more
particularly illustrating the main tubing hanger, and downhole
adjacent the reservoir, a torque anchor, outer housing, pup joint,
burner housing, burner nozzle and casing seal;
FIG. 14A is a quarter-sectional and elevation view of a further
step according to FIG. 13, more particularly illustrating the
insertion of the intermediate tubing string, hanging the tubing
from an intermediate tubing hanger, latching of the intermediate
mandrel and positioning of the oxygen passageway within the burner
housing;
FIG. 14B is a closeup of the burner interface assembly of FIG. 14A
for illustrating the intermediate tubing, the intermediate mandrel
and the oxygen passageway;
FIG. 15A is a quarter-sectional and elevation view of a further
step according to FIG. 13, more particularly illustrating the
insertion of the inner tubing string, hanging the inner tubing from
an inner tubing hanger, latching of the inner mandrel; and
FIG. 15B is a closeup of the burner interface assembly of FIG. 15A
for illustrating the hanging the inner tubing from the inner tubing
hanger, the inner tubing and the inner mandrel.
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, a thermal process utilizes a downhole
production of heat, steam and hot combustion gases (primarily CO,
CO.sub.2, and H.sub.2O) to best effect for the recovery of residual
or otherwise intractable hydrocarbons from a hydrocarbon reservoir
10. A burner assembly 20 initially creates a combustion cavity 30
and then creates and sustains the creation of hot combustion gases,
such as CO, CO.sub.2, and H.sub.2O. Addition of water to the
reservoir 10 above the combustion cavity 30 results in the
production of a steam drive front. The steam and hot combustion
gases combine to create a steam and gaseous drive front.
With further reference to FIGS. 1, 2B, 3, 4 and 13, apparatus for
implementing such a process comprises a burner assembly 20 at a
downhole end of a main tubing string 40 and one or more additional
tubing strings. The main tubing string 40 and other tubing strings
form a plurality of discrete fluid passageways for supplying the
burner assembly 20. As shown in FIG. 4, the downhole burner 60 is
terminated in an existing cased wellbore adjacent casing
perforations accessing the reservoir 10. The burner assembly 20 can
comprise a burner interface assembly 50 for fluidly connecting to
the tubing strings, a downhole burner 60, and a casing seal 70 for
sealing a casing annulus 80 between the downhole burner 60 and a
casing 90 of the cased wellbore. The casing annulus 80 is yet
another passageway used for directing water from the casing annulus
80 to the reservoir 10.
As shown in FIGS. 2A to 4, one approach is to suspend the burner
assembly 20 from a conventional sectional tubing string supported
by a conventional tubing hanger 100 on a wellhead 110. The casing
annulus 80 is formed between the casing 90 of the wellbore and the
main tubing string 40 and extends to the annular space between the
casing 90 of the wellbore and the burner assembly 20.
An intermediate tubing string 120 having an intermediate bore, such
as an intermediate coil tubing string, is supported by an
intermediate tubing hanger 130 on the wellhead 110 and disposed
within a bore of the main tubing string 40. An intermediate annulus
140 is formed between the main tubing string 40 and the
intermediate tubing string 120.
An inner tubing string 150, such as an inner coil tubing string, is
supported by an inner tubing hanger 160 on the wellhead 110 and is
further disposed within the intermediate bore of the intermediate
tubing string 120, forming a inner annulus 170 therebetween. The
inner tubing string 150 further has an inner bore 180.
The wellhead 110 and tubing hangers 100, 130, 160 can be any
appropriate wellhead and tubing hangers that are commonly available
in the industry, such as the thermal wellhead and tubing hangers
commercially available from StreamFlo Industries, Ltd., located at
Edmonton, Alberta, Canada. The casing annulus 80, the intermediate
annulus 140, inner annulus 170, and the inner bore 180 all define
discrete passageways for supplying the burner assembly 20.
The casing 90 of the cased wellbore, main tubing string 40, the
intermediate tubing string 120 and the inner tubing string 150,
creating the four discrete passageways, terminate at the burner
interface assembly 50. The casing annulus 80 terminates at the
downhole burner 60 for communication with the reservoir 10. The
inner annulus 170 terminates at the burner interface assembly 50.
The two remaining discrete passageways, the intermediate annulus
140, and inner bore 180, all connect or terminate at the downhole
burner 60.
In one embodiment, the downhole burner 60 implements at least two
fluid passageways for conducting fuel and oxidant for combustion.
The oxidant is a source of oxygen, conventionally air, or more
concentrated source such as a purified stream of oxygen. In a
preferred embodiment, purified oxygen is used as the oxidant
instead of conventional air, as conventional air produces
combustion gases having a substantial amount of gaseous nitrogen
products.
The burner interface assembly 50 fluidly connects two of the
discrete passageways to two fluid passageways of the downhole
burner 60. In one arrangement, a third discrete passageway can be
utilized as an isolating passageway between the fuel and the oxygen
for sensing or detecting leaks in the discrete passageways for the
fuel and oxygen.
The downhole burner 60 comprises a burner housing 190 having a
downhole portion 200 for the mixing of fuel and oxygen. The burner
housing 190 supports a high temperature casing seal 70 for sealing
the casing annulus 80 from the combustion cavity 30. The sealed
casing annulus 80 can be used to fluidly communicate water down to
the target zone, which is then injected into the reservoir 10 for
creating steam within the target zone, above the combustion cavity
30.
With reference to FIGS. 2A, 2B, and 3, one embodiment of the
present invention comprises the burner assembly 20 fluidly
connected to the main tubing string 40. A downhole burner 60 is
positioned at a downhole portion of a cased portion of an injection
well, the casing 90 being perforated into the reservoir 10. The
main tubing string 40 extends downhole and has conduits or
passageways for conducting or transporting each of fuel, and
oxygen, to the downhole burner 60. For ease of installation,
intermediate and inner tubing strings 120, 150 are releasably
connected to the burner assembly 20.
The downhole components, or as part of the burner assembly 20, can
further comprise a torque anchor 210 to set the main tubing string
40 in the casing 90.
In greater detail, and with reference to FIGS. 3 to 6, the burner
housing 190 is adapted at an uphole portion 220 for fluid
communication with the intermediate annulus 140 and inner bore 180.
In one embodiment, the burner housing 190 is fluidly connected to
the intermediate annulus 140 and the inner bore 180 through the
burner interface assembly 50. The burner housing 190 comprises two
fluid passageways for fluidly communicating the fuel and
oxygen.
As best shown in FIGS. 5 and 6, the burner housing 190 comprises
the downhole portion or burner nozzle 200 for combustion of the
fuel and oxygen and an uphole portion 220 defining the two fluid
passageways for fluidly communicating the fuel and oxygen to the
nozzle 200. The uphole portion 220 has a bore 230 and a concentric
conduit or tubing 240 extending therethrough for creating the two
fluid passageways. A fuel passageway 250 is defined by the annular
space formed between the bore 230 and the concentric conduit 240.
The concentric conduit 240 further has a bore defining an oxygen
passageway 260.
The fuel passageway 250 is adapted to fluidly communicate with the
intermediate annulus 140, communicating fuel from the surface to
the nozzle 200. The bore 230 of the burner housing 190 and the fuel
passageway 250 open into the nozzle 200 for injecting the fuel into
the nozzle 200. The fuel passageway 250 can further have fuel swirl
vanes 270 for aiding in the mixing of the fuel and oxygen.
The oxygen passageway 260 is in fluid communication with the inner
bore 180, communicating oxygen from the surface to the nozzle 200.
The oxygen passageway 260 has an opening 280 at a downhole end for
injecting oxygen into the nozzle 200. The oxygen passageway 260 can
further have oxygen swirl vanes (not shown) for aiding in the
mixing of the fuel and oxygen. The oxygen and fuel mix for
combustion at the nozzle 200.
With reference to FIG. 5, as stated above, the fuel passageway 250
can further have fuel swirl vanes 270 for imparting a rotation to
the fuel being injected into the nozzle 200. The oxygen passageway
260 can also have oxygen swirl vanes for imparting a rotation,
counter to the direction of the rotation of the fuel, for
maximizing the mixing of the fuel and oxygen for increasing the
efficiency of the combustion of the fuel and oxygen. In a preferred
embodiment, the ratio of swirl velocity to axial flow velocity of
either the fuel or oxygen is substantially 1:2.
In an alternate embodiment, the opening 280 of the oxygen
passageway 260 can be fitted with a bluff body (not shown) to
reduce the axial momentum of the oxygen for stabilizing the
combustion flame.
Further, in another alternate embodiment (not shown), the burner
housing 190 can have two side-by-side bores extending therethrough
for forming the fuel passageway and the oxygen passageway. Each
bore can have an opening at a downhole end for injecting the fuel
and oxygen into the nozzle 200 for combustion.
Conventional burner discharge arrangements can be employed
including utilizing a plurality of orifices and concentric
discharges. The nozzle 200 can be any open ended tubular structure
that allows mixing and combustion of the fuel and oxygen. As shown,
the nozzle 200 is a typical inverted truncated frusto-conical
nozzle. The truncated apex is fluidly connected to the burner
housing 190 and the nozzle 200 extends radially outwardly towards a
downhole end.
As shown in FIGS. 4 and 6, the high temperature casing seal 70 can
be located on the downhole burner 60 to isolate the casing annulus
80 from the combustion cavity 30. Accordingly, the casing seal 70
is generally located low on the downhole burner 60, such as between
the downhole portion of the burner housing or nozzle 200 and the
casing 90. In alternate embodiments (not shown), the casing seal 70
can located between the uphole portion 220 of the burner housing
190 and the casing 90.
Often, cased wellbores have casing distortions or kinks which
introduce challenges to installation and tolerances for related
seals to the casing. The casing distortions are an abrupt shifting
of the casing axis resulting in a casing portion that is narrower
than a nominal inner diameter of a typical casing. The passage of
seals and other downhole tools are difficult at best if the nature
of the seal is to initially comprise an outer diameter of seal
which is larger than the inner diameter of casing and certainly
greater than the distortion. Although downhole tools generally can
be manufactured to have a small outer diameter to allow them to
pass through a majority of distortions, seals generally can not.
Seals having small outer diameter, although capable of passing
through the distortions, are unlikely to fully seal against the
casing downhole of the distortion where the casing again has a
nominal inner diameter. Seals must also be able to withstand the
extreme heat conditions created by a downhole burner when
combusting the fuel and oxygen.
With reference to FIGS. 6 to 9, an embodiment of the casing seal 70
is a brush-type seal comprising a plurality of flexible,
concentric, metallic brush rings 300 stacked one on top of another.
As best shown in FIGS. 6, 7A and 7B, the brush rings 300 are
stacked one on top of another upon a circumferential stop shoulder
310 at a downhole end of the nozzle 200. Spacer rings 320 can be
provided to alternate between the brush rings 300. The stack of
brush rings 300 and spacer rings 320 is secured in place by a
compression ring 330 exerting an axial securing force to sandwich
the rings 300, 320 to the stop shoulder 310. A compression nut 340
secures the compression ring 330.
As shown in FIGS. 8 and 9, each seal ring 300 has a multiplicity of
slits 350 that are formed radially inward from an outer
circumference of the seal ring 300 and which terminate before an
inner diameter of the seal ring 300 for forming a plurality of
flexible fingers 360. The fingers are separated at the outer
circumference and connected at the inner diameter. An inner most
radial extension of each slit 350 defines the inner diameter of the
multiplicity of slits 350 and is substantially the same as the
outer diameter of the spacer rings 320. The plurality of fingers
360, flexing from the inner diameter, provide dimensional
variability through flexibility for each concentric seal ring
300.
Each slit 350 extends radially outwardly in a generally clockwise
direction as viewed looking downhole. This particular slit
arrangement or design is advantageous when removing and pulling up
the casing seal 70. In the event that the casing seal 70 becomes
stuck, the clockwise slit arrangement allows the casing seal to be
rotated in a counter-clockwise direction, thus decreasing the outer
diameter of the casing seal 70, and allowing it to dislodge from
the casing 90.
As shown in FIG. 9, each seal ring 300 can be rotationally indexed
relative to each adjacent seal ring 300. While enabling radial
flexibility, the slits 350 provide an avenue for fluids to leak
therethrough. In order to minimize the amount of leaking of fluids
through the slits 350, each seal ring 300 is rotated such that the
slits 350 of axially adjacent brush rings 300 are rotationally
offset or misaligned. To further mitigate leakage through the slits
350, the plurality of concentric brush rings 300 are stacked. Each
finger 360 of one seal ring 300 overlaps each finger 360 of an
adjacent seal ring 300, for forming a tortuous axial path for
restricting flow of casing annulus fluids therethrough.
Referring back to FIG. 7A, the brush seal 70 has an outer diameter
greater than a nominal inner diameter of a casing 90 in a cased
wellbore as indicated by the dashed line. The greater outer
diameter defines the effective sealing diameter of a particular
brush seal. Brush-type seals having differing effective sealing
diameters can be readily installed depending on the size of the
casing 90 in the cased wellbore.
When the brush-type seal is run downhole, each finger 360 of each
seal ring 300 flexes uphole, reducing the overall outer diameter
and conforming to the casing 90, while maintaining the effective
sealing diameter. The reduction of the overall outer diameter of
the brush rings 300 allow the brush seal 70 to pass through a cased
wellbore during installation and pass by most casing distortions.
Upon encountering a casing distortion, the ring fingers 360 of each
concentric seal ring 300 can elastically flex an additional amount
to enable movement past the distortion.
In an alternate embodiment, other casing seals might be employed
including a metallic inflatable packer, such as those now
introduced by Baker Oil Tools, as presented in a paper entitled
"Recent Metal-to-Metal Sealing Technology for Zonal Isolation
Applications Demonstrates Potential for Use in Hostile HP/HT
Environments", published as SPE 105854 in February 2007. Such
inflatable packers are small enough in diameter to also pass
through casing distortions and may be able to withstand the extreme
heat conditions created by the burner. However, such packers can be
damaged by thermal cycling and may not be reusable.
For example, in a 7 inch (178 mm) casing having an inner diameter
of about 164 mm, a burner bottom hole assembly (BHA) fluidly
connected to the downhole end of a 31/2 inch (89 mm) tubing, can be
placed in a cased wellbore having the typical casing distortions.
The burner BHA, comprising the burner interface assembly, pup
joint, and downhole burner, had a total length of about 5 feet
(1524 mm). A 23/8 inch (60 mm) intermediate coil tubing was
disposed within the 31/2 inch (89 mm) tubing, and a 11/4 inch (32
mm) inner coil tubing was disposed within the intermediate coil
tubing. The burner interface assembly was about 708 mm long and had
an outer diameter of about 114 mm, while the burner housing was
about 304 mm long with an outer diameter of about 93 mm. The brush
seal had an outer diameter of about 164 mm and was installed on a
nozzle having a circumferential shoulder of about 120 mm. Each
brush ring and spacer ring had a thickness of about 0.25 mm. The
pup joint, tailored to this particular example, was about 508 mm
long and had an outer diameter of about 27/8 inches (73 mm).
With reference to FIGS. 3 and 10, the fluid passageways can be
formed by a series of tubing strings disposed in the bore of a
larger tubing, or sectional tubing. Alternatively, two or more
tubing strings might be arranged side-by-side (not shown). As shown
in FIG. 3, the main tubing 40 is run down the cased wellbore
forming the casing annulus 80 or a first casing annular fluid
passageway therebetween. The intermediate tubing string 120 is
disposed concentrically within the bore of the main tubing string
40, forming the intermediate annulus 140 or a second intermediate
annular fluid passageway therebetween. The inner tubing string 150
is further disposed concentrically within the intermediate bore of
the intermediate tubing string 120 forming the inner annulus 170 or
a third inner annular fluid passageway therebetween. The bore of
the inner tubing string 150 further defines the inner bore 180 or a
fourth, inner bore fluid passageway.
Those skilled in the art would understand that although the
intermediate tubing string 120 is concentrically disposed with the
bore of the main tubing 40, the intermediate tubing string 120 may
not remain concentrically aligned within the bore of the main
tubing 40 as the intermediate tubing string 120 is run downhole.
Similarly, the inner tubing string 150, although concentrically
disposed in the intermediate bore of the intermediate tubing string
120 may not remain concentrically aligned as the inner tubing
string 150 is run downhole.
In a basic form, two passageways are used for providing fuel and
oxygen to the burner. A third passageway can be provided for
isolating the fuel and oxygen, and even more favourably for acting
as a sensing passageway for determining development of a leak
therebetween.
With reference to FIGS. 10 to 12, in one embodiment, a burner
interface assembly 50 fluidly connects three passageways of the
main tubing 40 to the fuel and oxygen passageways 250, 260 of the
downhole burner 60. The burner interface assembly 50 can comprise
an outer housing 400 secured intermediate or at the downhole end of
the main tubing string 40, an intermediate mandrel 410 at a
downhole end of the intermediate tubing string 120, and an inner
mandrel 420 at a downhole end of the inner tubing string 150.
The outer housing 400 has a bore which is adapted to releaseably
connect with the intermediate mandrel 410. The intermediate mandrel
410 has an uphole portion 430 having a bore which is adapted to
releaseably connect with the inner mandrel 420.
In greater detail, and with reference to FIG. 11, the outer housing
400 has a bore, an uphole end 440 and a downhole end 450. The
uphole end 440 is adapted to fluidly connect to the main tubing
string (not shown) and the downhole end 450 is adapted to fluidly
connect to a pup joint which supports the downhole burner (not
shown).
With reference to FIGS. 10 and 11, the intermediate mandrel 410 is
fit within the bore of the outer housing 400 forming the
intermediate annulus 140 therebetween. The intermediate mandrel
410, releaseably connected to the outer housing 400 at an
intermediate latch assembly 470, has an uphole portion 430 which is
adapted to fluidly connect to the intermediate tubing string 120.
The uphole portion 430 further has a bore for releaseably
connecting to the inner mandrel 420. In one embodiment, the uphole
portion 430 is an inner latch housing.
The bore of the outer housing 400 has an inner surface 480 for
forming a first intermediate latch 470A. The first intermediate
latch 470A is formed adjacent a downhole end of the outer housing
400.
Further, the intermediate mandrel 410 has a second intermediate
latch 470B formed at its downhole end. The second intermediate
latch 470B is adapted to releaseably connect to the complementary
first intermediate latch 470A to form the intermediate latch
assembly 470.
With reference to FIGS. 10 and 12, the inner mandrel 420 is fit
within the bore of the inner latch housing 430 and releasably
connects with the intermediate mandrel 410 at an inner latch
assembly 490. Similar to the intermediate latch assembly 470, the
inner latch assembly 490 comprises a first inner latch 490A and a
complementary second inner latch 490B.
As shown, the intermediate mandrel 410 is fit within the bore of
the outer housing 400 for latching at the intermediate latch
assembly 470 and sealing at a first seal 500 therebetween. The
inner mandrel 420 is fit within the bore of the inner latch housing
430 for latching at the inner latch assembly 490 and sealing at a
second seal 510 therebetween.
The intermediate annulus 140 is contiguous with an annular space
between the outer housing 400 and the intermediate mandrel 410 and
is in fluid communication with the fuel passageway 250 of the
downhole burner 60. The inner bore 180 is contiguous with a bore of
the inner mandrel 420 and is in fluid communication with the oxygen
passageway 260 of the downhole burner 60. In this embodiment, the
inner annulus 170 happens to terminate sealably at the second seal
510 for isolating the intermediate annulus 140 from the inner bore
180.
The sealed inner annulus 170 isolates the intermediate annulus 140
from the inner bore 180. This separation of the two discrete
passageways provides a safety measure, ensuring that the fuel and
the oxygen are separated by a buffer. In one embodiment, the sealed
inner annulus 170 is also a sensing annulus for detecting leakage
in the transport of the fuel and the oxygen. The sealed inner
annulus 170 can be maintained in a vacuum or other pressure and is
monitored for determining change in pressure indicative of a leak
in either the intermediate annulus 140 or the inner bore 180.
The intermediate latch assembly 470 can be any suitable releasable
latch used in the industry, but in a preferred embodiment, the
intermediate latch assembly is a type of latch assembly disclosed
and claimed in U.S. Pat. No. 6,978,830, issued on Dec. 27, 2005, to
MSI Machineering Solutions, Inc., located in Providenciales, Turks
and Caicos.
Similar to the intermediate latch assembly 470, the inner latch
assembly 490 can be any suitable latch assembly used in the
industry, including that disclosed and claimed in the
aforementioned U.S. Pat. No. 6,978,830.
As best shown in FIG. 12, an uphole end of the inner latch housing
430 is fit with a third seal 520 for sealing and isolating the
intermediate annulus 140 from the inner annulus 170. The inner
latch housing 430 further has a second seal 510 for sealing and
isolating the inner annulus 170 from the inner bore 180.
For redundancy purposes, and to ensure sealing and isolating of the
three discrete passageways, the first, second, and third seals 500,
510, 520 can be a plurality of individual seals in a stacked
arrangement.
For greater safety and control of the fuel and oxygen passageways,
and in a particular embodiment, the intermediate mandrel 410 can
further comprise a backpressure valve assembly 600 for controlling
the flow of the fuel and oxygen. Fuel is forced from the
intermediate annulus 140 through the backpressure valve assembly by
the first seal 500.
The backpressure valve assembly 600 comprises two fluid bypass
passageways, each having a backpressure valve. The fluid bypass
passageways bypass the first seal 500. A first bypass passageway
610, having a first backpressure valve 620, is in fluid
communication with the intermediate annulus 140 for transporting
the fuel from the main tubing string 40 to the fuel passageway 250
of the downhole burner 60. A second bypass passageway 630, having a
second backpressure valve 640, is in fluid communication with the
inner bore 180 for transporting the oxygen to the oxygen passageway
260 of the downhole burner 60.
Each of the backpressure valves comprises a ball 620A, 640A and a
spring 620B, 640B, biased to apply a constant closing force on the
ball, ensuring that the ball is sealingly fit within a ball seat
650A, 650B. The constant closing force is greater than the force
applied by the differential fluid pressure between the static fluid
pressure above the backpressure valves 620, 640 and a reservoir
pressure below the backpressure valves 620, 640. For either the
fuel and/or oxygen to flow pass the backpressure valves 620, 640,
the injection pressure of the fuel or oxygen must exert enough
force to overcome the combined forces of the spring 620B, 640B and
the reservoir pressure.
In one embodiment, the closing force biasing the ball of the
backpressure valves 620, 640 is based upon a differential pressure
of 200 psi. In this embodiment, the injection pressure of both the
fuel and oxygen must be sufficient to exert sufficient pressure to
overcome the combined forces of the closing force and the force
exerted by the reservoir pressure.
The injection pressure of the fuel or oxygen does not exceed the
fracturing pressure of the particular target zone.
In Operation
In one embodiment, a combustion chamber 30 is formed by melting a
target zone at a temperature sufficient enough to melt the
hydrocarbon reservoir 10 at the target zone. Thereafter, a steady
state combustion is maintained for sustaining a sub-stoichiometric
combustion of the fuel and oxygen for producing hot combustion
gases (primarily CO, CO.sub.2, and H.sub.2O) which enter and
permeate through the reservoir 10. The hot combustion gases create
a gaseous drive front and heat the reservoir 10 adjacent the
combustion cavity 30 and the wellbore.
Addition of water to the reservoir 10 along the casing annulus 80
above the combustion chamber 30 injects water into an upper portion
of the reservoir 10 adjacent the wellbore for lateral permeation
through the reservoir 10. The lateral movement of the injected
water cools the wellbore from the heat of the hot combustion gases
and minimizes heat loss to the formation adjacent the wellbore. The
water further laterally permeates through the reservoir 10 and
converts into steam. The steam and the hot combustion gases in the
reservoir 10 form a steam and gaseous drive front.
In more detail and referring again to FIGS. 1, and 13-15B, an
injection well is cased and perforated at a target zone of the
reservoir 10.
A packer is set and a suitable depth of thermal cement is placed
below the target zone. The thermal cement protects the packer from
the downhole burner 60.
Referring to FIG. 13, a first main tubing hanger 100 is affixed to
a wellhead 110. A burner bottom hole assembly (burner BHA) 700
comprising a torque anchor 210, the outer housing 400 of the burner
interface assembly 50, a pup joint 710, and the downhole burner 60
are fluidly connected to a downhole end of a main tubing string 40.
The burner BHA 700 is run downhole to a depth for positioning the
downhole burner 60 within a target zone. In one embodiment, the
downhole burner 60 is positioned at about the midpoint of the
target zone. Once in position, the main tubing string 40 is rotated
to set the torque anchor 210 and the main tubing string 40 is hung
from the main tubing hanger 100.
As shown in FIGS. 1 and 3, the main tubing string 40 and the casing
90 of the wellbore form a casing annulus 80 therebetween. The
casing seal 70 between the burner housing 190 and the casing 90
seals the casing annulus 80.
Referring to FIG. 14B, an intermediate tubing hanger 130 is
supported on the main tubing hanger 100. With reference to FIGS.
14A and 14B, the intermediate mandrel 410 is fluidly connected to a
downhole end of the intermediate tubing string 120, and the
concentric tubing 240 defining the oxygen passageway 260 extends
downhole from the intermediate mandrel 410. As shown in FIG. 14B,
the intermediate tubing string 120 is run downhole within the bore
of the main tubing string 40. The intermediate mandrel 410 is run
downhole until it is tagged with the outer housing 400 of the
burner interface assembly 50. Tagging the intermediate mandrel 410
to the outer housing 400 involves releaseably connecting the outer
housing 400 to the intermediate mandrel 410 at the intermediate
latch assembly 470, forming the intermediate annulus 140
therebetween. The intermediate tubing string 120 is pulled uphole
to stretch the intermediate tubing 120 and remove any slack. The
intermediate tubing string 120 is hung by the intermediate tubing
hanger 130 and then cut to an appropriate length.
With reference to FIG. 15A, an inner tubing hanger 160 is supported
on the intermediate tubing hanger 130. The inner mandrel 420 of the
burner interface assembly 50 is fluidly connected to a downhole end
of the inner tubing string 150, and run downhole within the
intermediate bore of the intermediate tubing string 120. The inner
tubing string 150 is run downhole until the inner mandrel 420 tags
the intermediate mandrel 410 forming the inner annulus 170. Tagging
the inner mandrel 420 to the intermediate mandrel 410 involves
releaseably connecting the inner mandrel 420 to the intermediate
mandrel 410 at the inner latch assembly 490. The inner tubing 150
is pulled uphole to stretch the inner tubing 150, hung by the inner
tubing hanger 160 and then cut to an appropriate length. The bore
of the inner tubing string 150 defines the inner bore 180.
The intermediate annulus 140 can be fluidly connected to a source
of fuel, and the inner bore 180 can be fluidly connected to a
source of oxidant, such as oxygen. The inner annulus 170 is sealed
and is monitored. Any changes with the pressure within the sealed
inner annulus 170 are indicative of a leak in either the
intermediate annulus 140 or the inner bore 180.
A further utility of the backpressure valve assembly is to assure
successful latching and continuity of the intermediate and inner
tubing string at the burner interface assembly, an inability of the
either passageway to retain pressure up to the opening pressure of
the valves being indicative of a problem in the connections of one
form or another.
The fuel can be delivered down the intermediate annulus 140 passing
through the first bypass passageway 610 and first backpressure
valve 620 and to the fuel passageway 250. Similarly, oxygen can be
injected down the inner bore 180, through the second bypass
passageway 630 and the second backpressure valve 640 to the oxygen
passageway 260. Both the fuel and oxygen enter the nozzle 200 for
combustion. The first and second backpressure valves 620, 640
creates a backpressure greater than that static head to surface
pressure, ensuring that the flow of the fuel and oxygen can be
controlled from the surface by controlling the flow rate of the
fuel and oxygen. If the flow rate of the fuel or oxygen does not
create enough pressure to overcome the pressure exerted by the
closing force of the backpressure valve spring 620B, 640B and the
reservoir pressure, fuel and oxygen cannot pass the first and
second backpressure valves 620, 640.
After the burner assembly 20 is positioned within the target zone,
the reservoir 10 can be initially flooded with water. Water is
injected down the casing annulus 80 to enter the reservoir 10
through the perforations for increasing the reservoir pressure
adjacent the wellbore. The fuel is then injected downhole. After a
sufficient amount of time to ensure that the fuel has entered the
target zone downhole, the fuel is doped with an accelerant, a
pyrophoric compound such as triethylborane or silane, sufficient
for igniting the fuel. Oxygen is injected to light off the downhole
burner 60. The accelerant is discontinued to create a stable flame
for combustion. A stable flame can be maintained by controlling the
rate of the fuel and oxygen. The fuel and oxygen are controlled to
combust at a temperature to create a combustion cavity 30
sufficient to melt or otherwise form a cavity 30.
In one embodiment, the downhole burner 60 can be lit off and form a
minimum stable flame temperature of about 2800.degree. C. At such a
temperature, it is believed that the casing 90 and the surrounding
reservoir 10 downhole of the burner 60 would melt, forming the
combustion cavity 30. As the combustion cavity 30 expands, molten
material will flow and pool at a bottom of the combustion cavity 30
above the thermal cement for forming an impermeable glassy bottom.
Further, the heat from the flame continues to be transferred to the
lateral walls by a combination of radiant heat transfer and hot
combustion gases permeating into the reservoir 10. Melting and
enlargement of the combustion cavity 30 ceases when the combustion
cavity 30 is sufficiently large enough that the heat transfer from
the combustion is below the melting point of the reservoir 10. The
lateral walls of the combustion cavity 30 remain porous and
permeable, perhaps in a sintered state.
Once the combustion cavity 30 has been formed, the fuel and oxygen
are controlled to continue steady state combustion for creating and
sustaining hot combustion gases for flowing and permeating into the
target zone.
Further, the steady state combustion of the fuel and oxygen is also
under sub-stoichiometric conditions, limiting the amount of oxygen
available for combusting with the fuel. The limited amount of
available oxygen ensures that there is no excess oxygen available
for flowing into the reservoir 10. Excess oxygen flowing into the
reservoir 10 may result in additional combustion within the
reservoir 10 and result in some coking therein.
Water is delivered down the casing annulus 80. The casing seal 70
directs the water out the perforations and into the target zone
concurrently as hot combustion gases are created and sustained at
steady state. The injected water and hot combustion gases in the
target zone interact to form a drive front comprising steam and hot
combustion gases.
The present process further protects the reservoir 10 from
permeability degradation due to chloride scaling by keeping the
chlorides in solution. Most chloride scaling is caused by
introducing water with a dissimilar ion charge during water
flooding. Increasing temperature and/or pressure typically improves
solubility of chlorides. The risks of chlorides deposition are
reduced as both temperature and pressure increase with the
introduction of heat and CO.sub.2 (from the hot combustion gases).
Higher CO.sub.2 concentrations in formed emulsion increases
carbonate solubility. The process can be operated to continually
produce incremental CO.sub.2, gradually increasing concentrations
as the flood progresses.
Risk of chloride scaling is further mitigated by maintaining an 80%
steam quality downhole which keeps chlorides in solution. Untreated
produced water typically contains upwards of 50,000 ppm of total
dissolved solids, which is typically treated prior to being passed
through boilers for conventional stem flood processes. Control of
the mass and heat balance of the combustion process permits
management of the steam generation in the target zone to be at
about 80% steam quality. The lower steam quality ensures that there
is a sufficient water phase to keep all dissolved solids in
solution and treatment of the produced water is not required.
In an alternate embodiment, fuel can be injected downhole through
the inner bore 180, while the oxygen can be injected down through
the intermediate annulus 140.
Further, in an alternate embodiment, where regulation may prohibit
injection of fluid down the casing annulus 80, water can be
injected down one of the other passageways. For example, water
could be injected down the intermediate annulus 140 for injection
at the burner assembly for communication with the hydrocarbon
reservoir. In such an embodiment, the inner annulus 170 can be used
to inject fuel or oxygen, instead of being used as a sensing
annulus for detecting leaks, oxygen or fuel could continue to be
injected down in the inner bore 180. Further, as those skilled in
the art would understand, the intermediate annulus 140 would have a
water injection port in the burner assembly and placed in fluid
communication with the reservoir to allow the injected water to
flow into and permeate through the reservoir and a flow through
packer can be used to isolate the burner assembly 20. One approach
is to locate a flow-through packer at about the burner assembly for
sealing the casing annulus above the water injection port. Water
injected from the intermediate annulus would exit from the water
injection port and into an injection annulus formed in the casing
annulus between the packer and the casing seal.
Further still, yet, in a further alternate embodiment, the inner
tubing string 150 can be eliminated such as to reduce costs. In
such an embodiment, the main tubing string 40 can be disposed
within the casing 90 forming the casing annulus 80, and the
intermediate tubing string 120 can be disposed in the main tubing
string 40 forming the intermediate annulus 140. The intermediate
tubing string 120 would have a bore forming the inner bore 180.
This embodiment would not have the inner annulus 170 to serve as a
sensing annulus for detecting leaks in the intermediate annulus 140
and/or the inner bore 180.
* * * * *